Microdevices based on micron and millimeter scale microelectro-mechanical systems (MEMS) technology are widely used in valve-containing microfluidic controls systems, microsensors, and micromachines. Currently, MEMS valves are used in automobiles, medical instrumentation, or process control applications, and in conjunction with appropriate sensors can provide accurate determinations of pressure, temperature, acceleration, gas concentration, and many other physical or chemical states. Microfluidic controls include microvalves for handling gases or liquids, flow gauges, and ink jet nozzles, while micromachines include microactuators, movable micromirror systems, or tactile moving assemblies. In part because of the ease of associating and integrating electronic control circuitry (using VLSI techniques), microdevices are commonly constructed from glasses or semiconductor material substrates such as crystalline silicon, commercially available in the form of semiconductor wafers used for production of integrated circuits.
Unfortunately, such wafer type substrates are not only rigid and somewhat brittle, but are also limited in size, generally having a circular diameter of only about 10 to 20 centimeters. Since many potential applications of MEMS require arrays of microdevices distributed on a meter scale, significant costs are associated with construction, distribution, attachment, and interconnection of large microdevice arrays based on silicon substrates. This is of particular concern in connection with large scale control of fluid flow using valve arrays such as would be expected in meter scale control arrays for paper transport. Such large scale fluid valve arrays are useful for numerous applications, including distributed actuator controls, paper or object positioning, dynamic control of fluid instabilities, construction of fluid actuated tactile displays, or microcontrol of microchemical reactions and biological assays. However, correctly positioning, mounting, and supplying power and control address lines to tens of thousands of fluid valves in meter scale arrays is expensive and unreliable. What is needed is a low cost and reliable microdevice construction method and system for supporting and controlling microdevice valves and sensors.
Large arrays of valves have particular utility in conjunction with a paper transport device or other material processing system that must often precisely control position and velocity of paper or other objects moving through the system. Commonly, material processing systems control object movement by physically engaging the object with a separate object drive mechanism that moves the object at a predetermined velocity along a predetermined path. For example, gear driven ratchets, rollers, hooks, or conveyors are widely employed to move objects as diverse as paper, semiconductors, plastics, or steel by mechanically engaging the objects, and moving the engaged objects along a desired path at a fixed velocity. While commonplace, mechanical or frictional engagement of objects does have a disadvantage of requiring direct physical contact with an object. For certain applications, including processing of high purity or delicate materials, contamination or damage to the object may result from mechanical grasping or contact. This is particularly true for high speed processing systems, which may damage objects simply by engaging them. For example, high speed rollers may damage paper through differential engagement of misaligned paper with the roller, resulting in ripping or tearing of the paper.
Fortunately, mechanical or frictional engagement is only one possible means for moving an object. Object drive mechanisms based on various fluid support techniques have long been employed to move delicate objects without requiring solid mechanical contact. For example, instead of using conventional belts, conveyors or rollers, paper moving through xerographic copier systems can be supported on a laminar air flow, or uplifted and moved by directed air jets. This form of fluid support is particularly advantageous, for example, when sheets of paper carrying unfixed toner images must be moved between a photoconductive drum and a fusing station where the toner image is fixed. With conventional physical rollers, the continuing possibility of dynamic distortions to the toner image, or even slight misalignments resulting in image degradation, must always be considered. Problems with image degradation are particularly acute with color images, which must register multiple overlays created by separate color toner/fuser processing cycles to create the color image.
However, previous attempts to use fluid transport in high speed material processing systems that require accurate positioning have not been very effective. The disadvantages of commonly available fluid transport systems that use air jet mechanisms for support is most apparent when flexible objects such as continuous rolls of paper, sheets of paper, extruded plastics, metallic foils, wires, or optical fibers are transported. In such systems, the flexure modes can result in complex object behavior. Unlike rigid objects, flexible objects are dynamically unstable when supported by air jets, with edge curl, flutter, or other undesirable dynamic movements continuously occurring during support and transport. Such undesirable movements of the flexible object can result in mispositioning, transport failure, or even damaging surface contact between the flexible object and an air jet conveyor.
Accordingly, the present invention provides novel valve structures for use in a fluid transport apparatus. The valves of the present invention can effectively work with either continuous or discrete flexible objects moving through a materials processing system. A sensor unit is used to sense motion state of flexible object, where motion state is defined to include position, orientation, curvature, speed, or other desired positional or velocity information. A motion analysis unit is connected to the sensor unit to calculate trajectory of the flexible object during transport based on its sensed motion state. Trajectory calculations can include determination of overall object position, velocity, and orientation information, as well as position, velocity, and orientation of subregions within the object (such as caused by flexure) To ensure for dynamic adjustments necessary for transport of the flexible object, a motion control unit is connected to the motion analysis unit, with the motion control unit configured to modify fluid flow directed against opposite sides of the flexible object to adjust motion state of flexible objects. This permits correction of object misalignments, incorrect speed or travel path, or object pitch, roll, and yaw (if three dimensional orientation information is available), and even unwanted flutter, buckling, or edge curling.
In a most preferred embodiment of the present invention, paper or other graphically markable material is among the flexible objects capable of being tracked in accordance with the present invention. A paper handling system includes a plurality of valved air jets adjusted for transport of paper, with at least a portion of the plurality of air jets being individually controllable. A sensing array continuously (or intermittently) determines paper position, and an air jet control unit connected to the sensing array is configured to modify paper trajectory in response to information received from the sensing array. In response to the calculated position, the air jet control unit modifies paper movement or orientation (for example, by selectively increasing or decreasing air flow from air jets that impart momentum to defined subregions of the paper) to nearly instantaneously correct for discrepancies in the motion state of the paper, including its position, orientation, trajectory, velocity, flexure, or curvature. In preferred embodiments, the plurality of opposed air jets can be used to apply tensile or compressive forces to flatten paper, and the air jet control unit can be used to maintain paper in this flattened position during transport. Of course, other paper positions (in addition to flat) can also be maintained, with, for example, the plurality of opposed air jets being used to generate sufficient force to curve selected subregions of the paper.
The present invention provides a practical alternative to the use of silicon wafer or glass substrates for valve construction and support in paper handling systems. A microdevice valve suitable for a paper handling system in accordance with the present invention can be constructed at least in part from a dielectric material forming a laminate, and is typically embedded within multiple laminate layers. The dielectric can be a fibrous, woven, extruded, or deposited polymer; a ceramic, or other dielectric material capable of being economically formed in meter scale sections. In a preferred embodiment, the laminate layer includes a dielectric base material and an impregnated bonding resin such as is commonly employed in conventional printed circuit board construction. The microdevice valve can be embedded in the laminate, and connected to at least one metallic electrical connection photolithographically formed on the laminate, with electrical connections allowing the device to be electrically powered and controlled. In certain embodiments, electroplated metals such as copper are bonded to form a part of the laminate that can be etched or otherwise modified to produce movable components. Such construction allows, for example, microdevice valves having flap, movable cantilever systems, or diaphragms. Advantageously, conventional etch techniques and materials developed for printed circuit board production can be modified for construction of novel microdevice valves according to the present invention. When dimensional stability or accurate spacing of large arrays of microdevice valves is important, the laminate can be rigidly constructed from woven glass and high bonding strength resins such as epoxies or polyimides. Conversely, if flexibility or smooth curves are needed in a particular application (e.g. an array of microvalved air jets for supporting objects moved in a tightly curved pathway), a flexible laminate constructed in part from polyimide, polyethylene terephthalate, aramid, or polyester dielectric films, and flexible polyester resins may be suitable.
Advantageously, the present invention allows for low cost batch construction of large scale arrays of microdevice valves for controlling paper transport, with meter scale constructions having hundreds of thousands of embedded microdevices being contemplated. The microdevice valves can be interconnected, or individually connected to power and control lines by photolithographically defined and etched leads. Typically, conventional printed circuit board construction techniques are used, with electrodeposited copper, adhesively attached and patterned as part of a photochemical etch process providing electrical connections for powering, controlling, or receiving sensed information from the microdevice valves. As will be appreciated, when extensive electrical connections are required, multilayer photolithographically etched boards can beneficially be used. In addition, movable or partially unsupported components can be defined by sacrificial etching techniques or other suitable MEMS batch processing techniques for undercutting or three dimensional shaping of components. Use of such sacrificial etching techniques in conjunction with printed circuit board laminates advantageously allows low cost construction of micron to millimeter scale valves, sensors, and conduit systems.
A particularly preferred embodiment of the present invention provides for microvalves embedded or attached immediately adjacent to conduits, passageways, or apertures defined in or supported by the laminate. The conduits allow fluid flow, while the microdevices embedded in the laminate intersect the conduits to provide either a valving or sensing mechanism for interacting with the fluid flow. Large scale arrays of microdevices for controlling fluid flow can be easily connected to centralized or distributed controllers by the photolithographically formed metallic electrical connections. In conjunction with appropriate sensors and fluid pressure sources, these arrays can be used to precisely control fluid flow, support objects such as paper, or even inject electrical charge, dyes, inks, or chemicals.
Additional functions, objects, advantages, and features of the present invention will become apparent from consideration of the following description and drawings of preferred embodiments.